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S TYLINOD ON                                     I 9 3

are double-ridged,, and that transversely to the long axis of the
jaw; finally, the much-worn teeth have flattish crowns more or
less surrounded by a ring of enamel.
A still later form, coming from the Lower and Middle Eocene
strata, is the genus Stylinodon. S. cylindrifer, which is the more
archaic of the two described species, is only known from a single
molar, fragments of a canine, and " some inconsiderable pieces of
the skull." The molar is interesting on account of the fact that
the enamel is still further reduced; it is represented only by
narrow vertical strips, which are much narrower than those of
older forms of G-anodonts. It is also hypselodont, and has a
persistent pulp. So, too, the canine which had a thick anterior
facing of enamel. The later species, S. minis, is more fully
known. The teeth seem to have been much the same as in the
last-described species ; the premolars and molars were seven in all
in the lower jaw, and the canine was imbedded in the bone for a
long distance, as in Calamodon. The cervical vertebrae have
short centra as in Semiganus. The clavicles were well developed.
The humeras possessed an entepicondylar foramen, and its head
displays the pyriform pattern so characteristic of later Edentates.
The foot is clearly like that of jPsittacotlieriutn.
In reviewing the series, therefore, we see a gradual diminution
of the incisors, a gradual loss of enamel on the teeth generally,
and the production of hypselodont teeth growing from per-
sistent pulps; all of which' are features of the later Edentates.
The progression is so gradual that the forms enumerated and
described seem to have been part of a continuous series cul-
minating in the Ground Sloths of later times. The other points
of similarity will be gathered from the facts given in the fore-
going pages.
There is another family belonging to the Ganodonta whose
position with regard to the Edentata is not so clear. This is
the family Conoryctidae, of which two genera are known. The
earliest of these, from the Lower Puerco, is Otiychodectes. In
O. t-issonensis the skull is long and narrow, thus contrasting with
that of the last family. The facial part is also long. The lower
jaw is much more slender. The molar formula was complete,
but there is some doubt as to the incisors. Xlie molars are
tritubercular.
The other known genus is Conoryctes,     Its skiill has a
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